Why do some airplane headphones have 2 Jacks instead of 1 everywhere else?

Question

Every time I go on a plane it is about a 50/50 chance between headphones with 1 jack or 2.

Why do some have 2 jacks? What is the function of it?

In: 21

Answer 1

For a deep dive into history, check your search engine of choice for pneumatic airline headsets.